U.S. Pat. No. 5,960,368 discloses a “wet” oxidation process for reducing the volume of low level radioactive and mixed waste to enable the waste to be more economically stored in a suitable repository, and for placing the waste into a form suitable for permanent disposal.
U.S. Pat. No. 6,444,276, hereby incorporated by reference, discloses a method for decontaminating a surface that includes the steps of bringing a surface of a component formed of an unalloyed steel or a low-alloy steel into contact with a solution containing an oxalic acid for dissolving a contaminated layer from the component.
One of the most common components containing nuclear waste is a waste tank. Retrieval of waste from nuclear waste tanks is described in, for example, “Tank Waste Retrieval, Processing and On-site Disposal at Three Department of Energy Sites: Final Report” National Research Council (2006) ISBN 978-0-309-10170-7.
As described therein, tank waste typically includes supernatant liquid, saltcake and sludge. Typically, in a first retrieval step called bulk waste retrieval, the supernatant liquid is removed using a transfer pump. The saltcake typically is dissolved in water. The resulting solution is then pumped in the same manner as the supernatant liquid. The sludge may be mobilized using larger mixer pumps that mix the sludge into a slurry by directing a jet of water into the waste layer, and this slurry also is pumped out.
What remains after this bulk waste retrieval is called residual waste. The residual waste often includes radioactive material on the internal surfaces of the tank above the level of waste in the bottom of the tank and wastes composed of agglomerated materials such as those in sludge that resist physical removal techniques, for example, zeolites and other metallic species.
Both physical and chemical technologies have been employed to retrieve residual waste. Oxalic acid has been used to dissolve sludge, but concerns have been raised as listed at page 38 of “Tank Waste Retrieval, Processing and On-site Disposal at Three Department of Energy Sites: Final Report.” National Research Council (2006).
This reference also notes that “[d]ownstream problems could be addressed by destroying oxalic acid and metal oxalates after tank cleaning” but notes issues with using oxidants such as ozone. See “Tank Waste Retrieval, Processing and On-site Disposal at Three Department of Energy Sites: Final Report.” National Research Council 103 (2006).
As opposed to nuclear waste removal, decontamination of nuclear power plants has used a Chemical Oxidation Reduction Decontamination (CORD) process to destroy oxalate chemistry during the chemical decontamination process. In the CORD process, oxalate-based chemistry solubilizes corrosion products at high temperatures, for example, approximately 195° F. After the corrosion products are solubilized and the reaction is complete, the oxalic acid chemistry is destroyed by oxidation leaving only the metals that are removed on ion exchange resin. These processes are used on the primary coolant loop (PCL) of the nuclear power plant for purposes of radiation dose-reduction, but have not been known for addressing wastes such as tank waste.